Cah. Biol. Mar. (2007) 48 : 9-16 The ciliate Orchitophrya stellarum viewed as a facultative parasite of asteriid sea stars William B. STICKLE1, Eugene N. KOZLOFF2* and Margaret C. HENK1 (1) Department of Biological Sciences, Louisiana State University, Baton Rouge, Louisiana, 70803-1715, USA (2) Friday Harbor Laboratories, University of Washington, Friday Harbor, WA, 98250, USA *Corresponding author: Fax: (1) 206 543 1273. E-mail:
[email protected] Abstract: Orchitophrya stellarum Cépède, 1907 is a ciliate that consumes sperm in the testes of male asteriid sea stars in the Pacific and North Atlantic oceans. Previous studies have reported its presence in smears and sections of testes, and we have also observed it in the spawn. This organism is easily cultured in seawater containing bacteria nourished by yeast extract or tissues from various marine invertebrates and the domestic chicken. During adaptation to culture conditions, the ciliates become smaller, the number of kineties is reduced, and the buccal cavity is shifted farther away from the anterior end. These changes are reversed if the ciliates are fed sperm of asteriid sea stars. Orchitophrya stellarum is therefore consi- dered to be a facultative parasite that can live indefinitely in situations where it can feed on bacteria and tissue detritus. It probably enters the testes of reproductively mature male sea stars by way of the gonopores. Resumé : Le cilié Orcitophyra stellarum vu comme un parasite possible des étoiles de mer astériide. Le cilié Orchitophrya stellarum Cépède, 1907, parfois trouvé dans les étoiles de mer asterides mâles dans les océans Pacifique et Atlantique Nord, se nourrit de spermatozoïdes.